Manufacture of galvanized steel sheets



Sept, 11, 1%34. I c LANGWORTHY ET AL 1,973,004

MANUFACTURE OF GALVANIZED STEEL SI- IEETS Filed Sept. 26 1953 7101/11/11!!!l Illlllllllllllllllll1111111111114 Rummag wmw mgnmxwgsmmmmmw. 4 a

. INVENTOR cfLaz yzaorffig {"Zzzykes ATTORATY Patented Sept. 11, 1934 Par mmirao'rnnn 0F GALVANIZED STEEL smears Application September 26, 1933, Serial No. 691,096 In Great Britain October 3, 1932 15 Claims.

This invention relates to improvements in the manufacture of galvanized steel sheets and to composite sheets for building purposes.

The chief object of this invention is to provide means to eliminate the causes of rust which hitherto have inevitably acted on and in the course of time destroyed iron and steel sheets treated by, for instance, the process of galvanizing.

A further object is to provide a fire resisting surface to such sheets so as to render them resistant to the well known effects of conductivity of both heat and cold. We have caused various tests to be made under exceptionally severe conditions in order to ascertain the durability of sheets made in accordance with this invention. In addition to tests by exposure to climatic conditions the utility of the invention has been further tested by exposure to heat combined with corrosive chemical agents and such sheets have been found to possess a resistance to corrosion beyond that which we anticipated. One important test; which was conducted for a continuous period of over twelve months, consisted in suspending sheets,

made in accordance with this invention, immediately over tanks containing a ,boilingsolution of hydrochloric and sulphuric acid. Upon examination after this period the zinc and steel core was found to be entirely unaffected. Ordinary galvanized sheets subjected to the same tests were utterly destroyed in three days and steel sheets protected by composite sheets but Without the zinc covering were destroyed in a short time. Steel sheets protected in the usual manner with fibre and bituminous coverings were destroyed by the heat and chemical fumes in about a week.

According to this invention a sheet of iron or steel which may be flat, corrugated, perforated or not, or in the form of latticed metal, is first coated with zinc by the process known as galvanizing. The sheet is then heated to a temperature sufficient to open the pores or expand the pin-holes in the zinc and to permit of them be-' ing filled when a coating of coal-tar, rubber, or bituminous composition or the like is applied under heavy pressure. After this coating is applied the top side of the sheet is spread with a mixture of clay, cement, asbestos fibre and flaked graphite mixed with water, or a silicate of soda solution. This latter mixture may be in the form of a felted sheet applied in the usual manner. On the under side of the sheet a substantially similar mixture or felted sheet is applied but cellulose fibre is employed in place of the asbestos fibre. Steam is then sprayed on the covering surfaces to assist maturation of the cement and to raise the temperature of the composition coverings for the purpose of reducing the viscosity of the interposed layer of bitumen or the like. The sheet is then consolidated under heavy pressure. The application of zinc to the iron 4 or steel sheet is to raise its resistance to corrosion and not to render these metals incorrosible. Obviously the thicker the coating of zinc the longer will the iron or steel core resist corrosion, but it is difiicult to satisfactorily apply a thick cover ing as this readily flakes off. In spite of the fact that zinc corrodes, zinc applied to iron and steel forms an alloy which without doubt materially raises the resistance to corrosion under many conditions of exposure; but when iron and steel sheets coated with zinc are exposed in the corrosive atmosphere of sulphurous, and sulphuric acids, present in manufacturing districts, and the corrosive effects of a moist salt atmosphere, such sheets are rapidly attacked, so that it is evident that valuable as zin'c undoubtedly is to form a protective alloy with iron and steel, further protection is essential to provide any degree of real permanence. The need for this additional protection is emphasized by the Well known fact that in immersing the iron or steel sheets in the molten zinc it has not been found possible to 85 avoid the formation of pores, pin holes or the like, which admit water and the corrosive substances that water dissolves from the air, thus in spite of the thickness of the steel or zinc coating rust is eventually formed, and the ultimate destruction of the sheet is only a question of time.

The principle of our invention is to preserve the zinc coating on the iron or steel sheets by bonding on the zinc coating radically different materials of a corrosion resisting character in such a manner that they will not separate, thereby economically producing a sheet that is fireproof, waterproof, not productive of condensation. a non-conductor of heat and cold, and absolutely incorrodible under all climatic conditions; the effective combination of. protective coverings of dif fering protective substances on the iron or steel core ensuring a longer life than could possibly be attained by sheets manufactured by the hitherto known methods.

It has been found that when steam, which may be superheated according to the temperature required, is applied in the manner to be hereafter described, it effects when under heavy pressure the binding together of materials of a differing hafibre admitting air, while any moisture is pre ture. Thus a mixture of clay, graphite, cement, or similar substance, with or without fibre, made into a composition with water, may be made to adhere to a coal-tar, rubber, or bituminous composition in the formation of a sheet having a zinc coated iron or steel core.

We have discovered that the addition of about fifteen per cent of flaked graphite in the layer of covering composition has the eifect of deflecting the suns rays, and in combination with the clay increases the resistance to fire. Further, condensation on the under side of the sheet is reduced, if not entirely obviated, when the covering mixture is blended with cellulose fibre. The structure of the cellulose fibre, which is in the nature of a series of tubes, readily absorbs any condensation, and this is subsequently rapidly evaporated by reason of the cellular structure of the cellulose vented from reaching the zinc or iron by the interp osed coating of bituminous substances compressed on to the zinc.

According to one method of carrying out this invention and as an example a sheet of iron or steel is first coated with zinc or a zinc alloy preferably by the process known as galvanizing and subsequently heated to a temperature which will open the pores or expand the pin holes in the zinc to permit of their being filled by bituminous composition or the like. This composition may be a coating of coal tar, rubber or bituminous composition or the like applied under heavy pressure. The iron or steel sheet employed may be fiat, corrugated or otherwise shaped or it may be a plain sheet. These sheets may be perforated with indentations or punched with holes or provided with countersunk holes of any shape and spaced to form any design. In order to form a covering for the top side of the sheet a mixture is spread on the bituminous composition or a felted sheet is applied on the bituminous composition. This covering mixture or felted sheet may be made from substantially equal parts of clay, Portland or other cement, and asbestos fibre or the like, with about fifteen per cent of flaked graphite mixed with water or a silicate of soda solution. In order to form a covering for the under side of the sheet a similar mixture or felted sheet is applied on the bituminous composition but in this case cellulose fibre or the like is substituted for the asbestos fibre. Obviously, the proportion of the above ingredients may be varied and the outer coatings may be of any thickness or of different or various thicknesses as may be desired. The upper coating may be thicker than the under coating, or vice versa. A jet of steam is then sprayed on to the surfaces of the covering composition to assist maturation of the cement and to raise the temperature of the composition coverings for the purpose of reducing the viscosity of the interposed layer of bitumen, to permit of filling the pores or pin-holes in the zinc and the pores in the composition, by compression, and to provide ,for the satisfactory adhesion. The sheet is then consolidated under heavy pressure and it will be found that after the moisture has evaporated an effective bond'is obtained between the zinc and the two covering materials or compositions.

The invention isillustrated in the accompanying drawing;in which:

Figure 1 is a broken perspective showing th formation of the sheet.

. Figure 2 is a sectional view of the same.

As illustrated, a. represents the metal, b the upper and lower zinc deposit, c-the bituminous composition on the zinc deposit, and d the upper and lower layers on the bituminous composition.

What we claim is:

1. A method of forming a composite sheet for building and other purposes wherein a sheet of iron or steel is first coated with zinc and then heated to a temperature to open the pores in the zinc to permit of their being filled by bituminous composition or the like such composition applied under pressure, said sheet having further applied thereto top and bottom coatings of fire resisting composition and the whole being subjected. to the action of steam and consolidated under pressure.

2 A process for the filling of pin holes or pores in a sheet galvanized or coated with zinc or the like consisting in having a rubber, coal tar or bituminous composition or the like applied when the sheet is heated to a temperature sufficient to open the pores or expand the pinholes in the zinc or like coating the said rubber, coal tar or bituminous composition being applied by pressure.

3. A method of forming a composite sheet for building purposes wherein a sheet of iron or steel is first coated with zincor the like by a process known as galvanizing, subsequently heated to expand the pores or pinholes in the zinc and coated with a bituminous or rubber composition or the like applied under heavy pressure and further coated with a composition consistingof clay, cement, flaked graphite and asbestos or cellulose fibre in a wet or plastic condition and finally subjected to the action'of steam and consolidated under pressure. I,

4. A process for forming a composite sheet for building or other purposes consisting in first heating a galvanized iron or steel sheet to open the pores in the zinc, and coating the sheet under pressure with a bituminous composition, said sheet being further! coated or covered with a mixture of clay, aluminous, Portland or other cement with flaked graphite and asbestos or cellulose fibre in a wet or plastic condition, said coatings being subjected to the action of steam to reduce the viscosity of the bituminous composition and consolidating the whole under heavy pressure.

5. A method of forming a composite sheet as claimed in claim 1 wherein the bituminous composition is preserved from the effects of the suns rays by a fire resisting composition subjected to the action of steam and consolidated under pressure.

6. A method of forming a composite sheet as claimed in claim 1, wherein the upper side of the sheet is coated or covered with a composition or with'felted sheet consisting of clay, cement, asbestos fibre or the like and flaked graphite mixed with water or a silicate of soda or like solution.

'7. A method of I forming a composite sheet as claimed in claim 1, wherein the upper coating consists of substantially equal parts of clay, cement and asbestos fibre with about 15 per cent of flaked graphite.

8. A method of forming a composite sheet as claimed in claim 1, wherein the under coating consists of a mixture or with felted sheet composed of clay, cement, cellulose fibre or the like and flaked graphite mixed with water or a silicate of soda or like solution.

Q. A method of forming a composite sheet as claimed in claim 1, wherein the under coating consists of substantially equal parts of clay, ce-- ment and cellulose fibre with about 15 per cent flaked graphite.

10. A composite sheet for building purposes 12. A composite sheet as claimed in claim 10, wherein the metal sheet is punched or perforated with holes; indentations or the like of any design and shape.

13. A composite sheet as claimed in claim 10, wherein the metal sheet is formed with holes or indentations, the holes or indentations providing projections on one or both sides of the sheet.

14. A composite sheet as claimed in claim 10, wherein the composition coverings on each side of the sheet are of unequal thickness.

15. A composite sheet or the like having a galvanized metal core protected by a rubber or bituminous composition and a covering consisting of a mixture of clay, cement, fibre or the like and flaked graphite.

.CYRIL FROUDE LANGWORTHY. HELEN HUGHES. 

